Patients will receive a standard 5 mCi dosimetric dose of fission-derived Iodine I 131 Tositumomab. Pharmacokinetic data for the primary endpoint analysis will be derived from testing done on blood samples drawn at 12 timepoints over the first 7 days following administration of the dosimetric dose. Whole body gamma camera images will be obtained on six days following the dosimetric dose. Organ and tumor dosimetry data will be generated from gamma camera counts of specific organs and tumor. All scans will be examined by an independent review panel to evaluate biodistribution of the radionuclide.